Chiral discrimination of inhalation anesthetics and methyl propionates by thickness shear mode resonators: new insights into the mechanisms of enantioselectivity by cyclodextrins.

The discrimination of the enantiomers of methyl lactate, methyl 2-chloropropionate, and the inhalation anesthetics enflurane, isoflurane, and desflurane in the gas phase has been performed using thickness shear mode resonators. The selective coating was a modified perpentylated gamma-cyclodextrin derivative dissolved in a polysiloxane matrix. A new model for the sorption of the chiral compounds into the cyclodextrin cavities and into the polymer matrix was established for the purpose of characterizing the sensor responses. This characterization included the fitting of the sensor responses (preferential and nonpreferential sorption) according to the model and extracting the characteristic parameters. In particular we attempted to explain the observed variation of the chiral discrimination factor alpha with changing analyte or cyclodextrin concentrations and search for an invariable parameter, characteristic for a certain analyte-cyclodextrin combination. The process of chiral or "molecular" recognition was thoroughly investigated.